This application is based on Japanese Patent Application No. 11-80426 filed on Mar. 24, 1999, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The invention relates to an apparatus and a method for processing images, as well as to a storage medium carrying data generated by programming the method, in particular a filtering procedure for screened halftone images.
2. Description of Related Art
A majority of printed matters or documents today contain images expressed in numerous minute halftone dots, i.e., halftone images. When a document image scanned by a scanner is printed, the Moire effect may develop depending on the relation between the spatial frequency of the halftone dots contained in the document image and the dither pattern cycle.
The conventional digital copying machine applies the smoothing process to a halftone dot region to soften the edges of halftone dots in order to prevent the Moirxc3xa9 effect while applying the edge enhancing process to character elements in order to reproduce the character elements more sharply. However, such a method cannot be effective when character elements exist in the halftone dot region. For example, if the smoothing process is applied to the halftone dot region where character elements exist, the recreation capability for the character elements drops. On the other hand, if the enhancement process is applied to the same area, the edges of minute dots are enhanced, so that the Moirxc3xa9 effect may develop to deteriorate the image quality.
A method of detecting character elements in the halftone dot region by means of the spatial filter has been known. The size of the spatial filter is chosen to be larger than the spatial frequency of the halftone dots so that the edges of the halftone dots would not be mistaken as the edges of the character elements. Consequently, the edges of character elements in the non-halftone dot region, for example, the edges of fine letters written on a white background cannot be detected precisely, same as the edges of halftone dots so that the character elements cannot be sharply reproduced.
It is an object of the present invention to provide an image processing apparatus including a receiving unit for receiving image data, a halftone dot detector for detecting a halftone dot region using the received image data, a first edge detector for executing edge detection over the detected halftone dot region using a derivative filter, and a second edge detector for executing edge detection over a non-halftone dot region other than the detected halftone dot region using a derivative filter with a size different from a size of the derivative filter.
A further object of the invention is to provide an image reading apparatus including an image reading unit for reading a document image and converting the document image into image data, an image processing unit for applying image processes containing edge enhancing process and smoothing process to the image data, and a transmission unit for transmitting the processed image data. Furthermore, the image processing unit includes a halftone dot detector for detecting a halftone dot region using the image data, a first edge detector for executing edge detection over the detected halftone dot region using a derivative filter, and a second edge detector for executing edge detection over a non-halftone dot region other than the detected halftone dot region using a derivative filter with a size different from a size of the derivative filter.
Still a further object of the invention is to provide an image forming apparatus including an image reading unit for reading a document image and converting the document image into image data, an image processing unit for applying image processes containing edge enhancing process and smoothing process to the image data, and an image forming unit for forming the processed image data on a printing medium. In addition, the image processing unit includes a halftone dot detector for detecting a halftone dot region using the image data, a first edge detector for executing edge detection over the detected halftone dot region using a derivative filter, and a second edge detector for executing edge detection over a non-halftone dot region other than the detected halftone dot region using a derivative filter with a size different from a size of the derivative filter.
Still a further object of the invention is to provide an image processing apparatus including a receiving unit for receiving image data, a halftone dot detector for detecting a halftone dot region using the received image data, a first edge enhancing unit for applying edge enhancement process to the detected halftone dot region using a derivative filter, and a second edge enhancing unit for applying edge enhancement process to a non-halftone dot region other than the halftone dot region using a derivative filter with a size different from a size of the derivative filter.
Still a further object of the invention is to provide an image reading apparatus including an image reading unit for reading a document image and converting the document image into image data, an image processing unit for applying image processes containing edge enhancing process to the image data, and a transmission unit for transmitting the processed image data. In addition, the image processing unit includes a halftone dot detector for detecting a halftone dot region using the image data, a first edge enhancing unit for applying edge enhancement process to the detected halftone dot region using a derivative filter, and a second edge enhancing unit for applying edge enhancement process to a non-halftone dot region other than the halftone dot region using a derivative filter with a size different from a size of the derivative filter.
Still a further object of the invention is to provide an image forming apparatus including an image reading unit for reading a document image and converting the document image into image data, an image processing unit for applying image processes containing edge enhancing process to the image data, and an image forming unit for forming the processed image data on a printing medium. Furthermore, the image processing unit includes a halftone dot detector for detecting a halftone dot region using the image data, a first edge enhancing unit for applying edge enhancement process to the detected halftone dot region using a derivative filter, and a second edge enhancing unit for applying edge enhancement process to a non-halftone dot region other than the halftone dot region using a derivative filter with a size different from a size of the derivative filter.
Another object of the invention is to provide an image processing method including the steps of receiving image data, detecting a halftone dot region using the received image data, executing edge detection over the detected halftone dot region using a derivative filter, and executing edge detection over a non-halftone dot region other than the detected halftone dot region using a derivative filter with a size different from a size of the derivative filter.
A further object of the invention is to provide an image processing method including the steps of receiving image data, detecting a halftone dot region using the received image data, applying edge enhancement process to the detected halftone dot region using a derivative filter, and applying edge enhancement process to a non-halftone dot region other than the halftone dot region using a derivative filter with a size different from a size of the derivative filter.
Another object of the invention is to provide a storage medium carrying data generated by programming an image processing method including the steps of receiving image data, detecting a halftone dot region using the received image data, executing edge detection over the detected halftone dot region using a derivative filter, and executing edge detection over a non-halftone dot region other than the detected halftone dot region using a derivative filter with a size different from a size of the derivative filter.
A further object of the invention is to provide a storage medium carrying data generated by programming an image processing method including the steps of receiving image data, detecting a halftone dot region using the received image data, applying edge enhancement process to the detected halftone dot region using a derivative filter, and applying edge enhancement process to a non-halftone dot region other than the halftone dot region using a derivative filter with a size different from a size of the derivative filter.
The objects, characteristics, and advantages of this invention other than those set forth above will become apparent from the following detailed description of the preferred embodiments, which refers to the annexed drawings.